Loan Amortization Sheet: Payments, Interest, and Balance

A loan amortization sheet is a schedule showing how each regular payment is divided between interest and principal, along with the remaining balance after each payment. Enter the loan amount, annual interest rate, and term below to estimate the monthly payment and total interest for a fixed-rate loan with monthly payments.

Formula

This calculator uses the standard level-payment formula for a fixed-rate loan. It assumes the same payment is due once per month and that interest accrues monthly at the annual percentage rate divided by 12.

• Monthly payment: M = round(P × r ÷ [1 − (1 + r)⁻ⁿ], 2)
• Total interest: I = M × n − P
• Monthly rate: r = APR ÷ 1,200
• Number of payments: n = term in years × 12

P is the starting loan principal in dollars, APR is the annual percentage rate entered as a percent, M is the monthly payment in dollars, I is the estimated total interest in dollars, and n is the number of monthly payments. The payment is rounded to cents before total interest is calculated, so the displayed total follows the rounded-payment method. A lender’s actual payment schedule may differ if its calculation, dates, fees, or rounding conventions differ.

Worked Example

Using the calculator’s default inputs—$20,000 principal, 8% APR, and a five-year term:

1. Convert the APR to a monthly decimal rate: 8 ÷ 1,200 = 0.0066667.
2. Convert the term to payments: 5 × 12 = 60 monthly payments.
3. Apply the payment formula: $20,000 × 0.0066667 ÷ [1 − (1.0066667)⁻⁶⁰] ≈ $405.53 per month.
4. Estimate total interest using the rounded payment: $405.53 × 60 − $20,000 = $4,331.80.

The results are an estimated monthly payment of $405.53 and estimated total interest of $4,331.80. The scheduled total of payments would be $24,331.80 under these assumptions.

Assumptions

• The interest rate remains fixed for the full modeled term.
• Payments are equal, made monthly, and treated as on schedule.
• Interest compounds monthly at APR divided by 12.
• The estimate excludes fees, taxes, insurance, PMI, escrow, and other charges because none are entered.

What an Amortization Sheet Shows

A full amortization sheet expands the payment calculation into one row per payment period. Common columns include the payment number or date, beginning balance, scheduled payment, interest portion, principal portion, and ending balance. The beginning balance for a period is the amount still owed before that payment. Interest is calculated on that balance; the part of the payment left after interest is applied to principal.

For example, with the default figures, the first month’s estimated interest is about $133.33 ($20,000 × 0.0066667). Of the $405.53 payment, roughly $272.20 reduces principal, leaving a balance near $19,727.80. The exact row can vary by a cent because a lender may calculate interest using daily balances or a different rounding method. As the balance declines, the interest portion generally shrinks and the principal portion grows, while the scheduled payment stays level.

When to Use the Sheet and How to Read It

An amortization schedule is useful for understanding the planned path of a loan balance, estimating interest over the scheduled term, and seeing how payment timing affects principal reduction. It can also help you inspect a lender-provided schedule, provided you compare the same principal, rate, term, payment dates, and fee treatment.

• Check the starting principal against the amount actually financed, not just a purchase price.
• Compare the payment amount and number of installments with the lender’s disclosure.
• Review the ending balance: after all scheduled payments, it should be approximately zero, subject to rounding or a final adjusted payment.
• Look at the cumulative interest column separately from the payment column; they answer different questions.

A schedule is a projection, not a record of transactions that have already occurred. If payments are late, skipped, changed, or supplemented with extra principal, the actual balance and interest can diverge from the original table. Use an up-to-date account statement for the current payoff balance; a scheduled ending balance is not necessarily a payoff quote.

Common Misunderstandings and Limits

One frequent misconception is that every payment reduces principal by the same amount. On a standard level-payment loan, the total payment is generally constant, but its split changes: earlier payments usually contain more interest because the balance is larger. Another misconception is that APR always produces an exact lender payment. APR is an annualized rate, but the lender’s contract may specify a different accrual convention, payment timing, or financed charges.

The calculator also treats the term in years as a whole schedule of monthly payments. Its formula does not model variable rates, irregular payment dates, daily simple interest, balloon payments, deferred payments, or changing installment amounts. The total-interest estimate subtracts the starting principal from the total of rounded scheduled payments; it does not add fees or other costs. If a loan has an adjustable rate, a payment may change and a single fixed-rate schedule cannot describe the full term.

Extra Payments and Comparing a Lender Schedule

Extra payments can change an amortization path, but their effect depends on how the servicer applies them. An additional amount may be applied to principal, held for a future payment, or handled according to the loan’s terms. A standard schedule should not be treated as proof that an extra payment will shorten a loan by a particular number of months. Ask the lender how extra funds are applied and request an updated schedule when needed.

When checking a supplied sheet, verify the assumptions before interpreting differences. A small discrepancy can result from cent rounding or the first payment date; a larger one may reflect a different amount financed, rate, term, payment frequency, or included charge. Compare like with like, and rely on the lender’s disclosure for the contractual payment and balance figures.

Frequently Asked Questions

What is a loan amortization sheet?
A table that lays out scheduled payments over a loan term, showing the interest and principal in each payment and the resulting balance.

How do I calculate an amortized monthly payment?
Convert APR to a monthly rate by dividing it by 1,200, convert years to months, then use the fixed-payment formula shown above. This calculator performs those steps and rounds the payment to cents.

Why does the interest portion decrease over time?
For a fixed-rate loan, periodic interest is based on the outstanding balance. As principal is repaid, the balance falls, so the interest portion typically falls too.

Does the sheet show the exact payoff amount?
No. A schedule estimates balances on planned payment dates. A payoff figure can include interest accrued since the last payment and other contract-specific amounts; request the current figure from the lender.

Can an amortization schedule include extra payments?
Yes, if the schedule is recalculated with the extra amounts and their application to principal is known. This calculator does not take extra payments as an input.

This result is an estimate for educational purposes; the lender’s disclosure gives the exact figures.

Related

• Loan Term Out? Calculate Monthly Payments and Interest
• Free Loan Amortization Calculator and Payment Schedule
• Free Loan Amortization Schedule Calculator

in p | Loan amount | $ | 20000 | 1 | 100000000
in apr | Interest rate (APR) | % | 8 | 0.01 | 100
in yrs | Loan term | years | 5 | 0.0833 | 50
out pmt | Monthly payment | $ | round(p * (apr / 1200) / (1 - (1 + apr / 1200) ^ -(yrs * 12)), 2) | 2
out int | Total interest | $ | pmt * yrs * 12 - p | 2